In a display device which displays video, a display device which displays video that is perceived in three dimensions, for example, alternately displays, in predetermined cycles (field cycles, for example), a left eye frame image (referred to as an L frame image hereinbelow) for viewing with the left eye and a right eye frame image (referred to as an R frame image hereinbelow) for viewing with the right eye. The L frame image and the R frame image thus displayed contain content which differs only in its parallax. The viewer views the L frame image and R frame image via a glasses device which includes a liquid crystal shutter which is driven in synchronization with L frame image display cycles and R frame image display cycles (see Japanese Patent Application Publication No. S62-133891 and Japanese Patent Application Publication No. 2009-25436, for example). As a result, the viewer perceives an object, rendered by the L frame image and R frame image, in three dimensions.
FIG. 37 is a block diagram of a conventional video viewing system. Note that 60 Hz video signals (left eye video signals and right eye video signals) are input to the video viewing system shown in FIG. 37.
The video viewing system 900 includes a video signal processor 901 to which the 60 Hz video signals (left eye video signals and right eye video signals) are input. The video signal processor 901 converts the video signals thus input into 120 Hz left eye video signals and 120 Hz right eye video signals. The converted left eye video signals and right eye video signals are output to a liquid crystal driver 902 and a backlight controller 903. The liquid crystal driver 902 converts the 120 Hz left eye video signals and right-eye video signals into a format which can be displayed by a liquid crystal panel 904. The left eye video signals and right eye video signals thus converted by the liquid crystal driver 902 are output to the liquid crystal panel 904. The backlight controller 903 outputs a light emission control signal to the backlight 905. The backlight 905 radiates light from the backside of the liquid crystal panel 904 onto the liquid crystal panel 904 by the light emission control signal. As a result, L frame images and R frame images are displayed alternately on the liquid crystal panel 904 at 120 Hz.
A glasses device 950 includes a left eye shutter 951 and a right eye shutter 952. A shutter control circuit 906 for the left eye shutter 951 and a shutter control circuit 907 for the right eye shutter 952 synchronously control the left eye shutter 951 and the right eye shutter 952 by taking the 120 Hz left eye video signals and right eye video signals thus converted by the video signal processor 901 as a reference.
FIG. 38 is a control timing chart of the conventional video viewing system 900. Section (A) in FIG. 38 shows the scanning timing for the L frame images and R frame images of the liquid crystal panel 904. Section (B) in FIG. 38 shows the timing for lighting the backlight 905. Section (C) in FIG. 38 shows the timing for opening and closing the shutters 951 and 952 of the glasses device 950. The conventional video viewing system 900 is described using FIGS. 37 and 38.
Left eye video signals and right eye video signals are sequentially written to the liquid crystal panel 904. Meanwhile, the backlight 905 is always lit. The shutter control circuits 906 and 907 control the shutters 951 and 952. After the alternate left and right write scanning to the liquid crystal panel 904, the shutters 951 and 952 open and close under the control of the shutter control circuits 906 and 907 such that the open cycles of the shutters 951 and 952 are half of the respective video cycles. The L frame images and the R frame images which are viewed via the shutters 951 and 952 are viewed by the viewer's left and right eyes respectively. As a result, the viewer generates a visually stereoscopic image in the brain.
In the video viewing system which operates with the control timing shown in FIG. 38, the viewer views an L frame image or an R frame image only in those cycles in which the shutters 951 and 952 are open (cycles which are sufficient for viewing the images required for the generation of a stereoscopic image). Meanwhile, even in those cycles which are not those cycles when the shutters 951 and 952 are open, the backlight 905 is always lit. Therefore, a video viewing system which operates with the control timing shown in FIG. 38 is unfavorable from the standpoint of power savings.
FIG. 39 is another control timing chart for the conventional video viewing system 900. Section (A) of FIG. 39 shows the scanning timing for the L frame images and R frame images of the liquid crystal panel 904. Section (B) of FIG. 39 shows the timing for lighting the backlight 905. Section (C) in FIG. 39 shows the timing for opening and closing the shutters 951 and 952 of the glasses device 950. The conventional video viewing system 900 will be illustrated further using FIGS. 37 to 39.
Japanese Patent Application Publication No. 2009-25436 discloses control in which the backlight 905 is lit only in those cycles when an L frame image or an R frame image is being viewed. In the control shown in FIG. 39, unlike the control shown in FIG. 38, the backlight 905 emits light only in those cycles when an L frame image or an R frame image is being viewed. Therefore, the control as shown in FIG. 39 is superior from a power savings standpoint than the control shown in FIG. 38.
The left eye shutter 951 is opened after the liquid crystal panel 904 has displayed an L frame image which is created for viewing by the left eye, and before scanning on the basis of a right eye video signal for displaying an R frame image is executed. Similarly, the right eye shutter 952 is opened after the liquid crystal panel 904 has displayed an R frame image which is created for viewing by the right eye, and before scanning on the basis of a left eye video signal for displaying an L frame image is executed.
As shown in FIGS. 38 and 39, scanning on the basis of the left eye video signal and/or right eye video signal is/are executed starting at the upper portion of the liquid crystal panel 904. Therefore, the scanning on the basis of the left eye video signal and/or right eye video signal at the lower portion of the liquid crystal panel 904 lags the scanning at the upper portion of the liquid crystal panel 904.
The response of the liquid crystals based on the left eye video signal and/or the right eye video signal takes time depending on the type of the video displayed. For example, if there is a large difference between the brightness of pixels rendering a frame image which is displayed beforehand and the brightness of pixels rendering a frame image which is displayed subsequently, a relatively long liquid crystal response time is required.
If the left eye shutter 951 or the right eye shutter 952 is opened while waiting for the display of an L frame image or R frame image to end, the time during which the left eye shutter 951 or the right eye shutter 952 is open is short owing to the fact that the liquid crystal response time is long. As a result, the three dimensional images displayed on the liquid crystal panel 904 appear dark to the viewer.
If the left eye shutter 951 is opened without waiting for the display of the L frame image to end, the viewer views an L frame image with the effects of the R frame image displayed beforehand mixed therein. If the right eye shutter 952 is opened without waiting for the display of the R frame image to end, the viewer views the R frame image with the effects of the L frame image displayed beforehand mixed therein. Such mixing of the L frame image and the R frame image is known as crosstalk. The amount of mixing of the preceding frame image (the L frame image or R frame image) is especially substantial at the lower portion of the liquid crystal panel 904 due to the lag of the scanning on the basis of the left video signal and/or right video signal at the lower portion of the liquid crystal panel 904 and to the liquid crystal response time. Therefore, it is hard for the viewer to perceive the frame images displayed in the lower portion of the liquid crystal panel 904 in three dimensions.
The above problems are not limited to display devices which display video that is perceived in three dimensions and can also be perceived in display devices which display normal two-dimensional video. That is, when effects of a preceding frame image which is displayed beforehand are mixed in a subsequent frame image which is displayed after the preceding frame image and crosstalk is generated, there is a reduction in quality of the displayed image.